My 2009 MacBook Pro has finally given up so I'm very tempted by the 12.9 Pro after seeing the Affinity photo app. My questions are
Does iOS allow the editing of RAW images?
Is there a way of transferring edited images from the iPad to an external hard drive?
I'm an avid amateur photographer and have been using a 12.9 inch iPad Pro as my only computer for over a year now. The process that works for me is to shoot RAW + JPEG fine and import using the SD card reader. I shoot RAW + JPEG because photos cannot edit raw files and if you only shoot raw you end up with the very low resolution embedded JPEG in photos that gets edited and shared in that app.
For RAW editing I've found Polarr to be the best solution for editing and workflows. Lightroom Mobile is just too limited, in my opinion.
As others have mentioned, I don't think you can back up to an external hard drive, but I pay for 1TB, I guess now it's 2TB, of iCloud storage and backup all my photos there.